Penguins come in numerous sizes, roughly akin to the calibre of the desired projectile weapon. For example, a small, man-portable weapon could be constructed on a similar scale to the modern bazooka, the barrel of which would be an ideal size for the expulsion of Adeliepenguins. The large (compared to a bullet) size of the Adelie would make this a formidable anti-infantry weapon, as few personal armours could offer protection against such a heavy projectile.

Further, at the other end of the scale, it would be possible to craft an enormous artillery piece, outweighing even the largest explosive cannons, built to accommodate the vast bulk of the Emperor penguin. Such a weapon would be of primary use against buildings and enemy tanks, as well as demoralising the enemy's ground troops. Soldiers are hardened against explosions and incoming shells, but a man's heart would soon quail if his base of operations were suddenly awash with penguin gore and entrails.

The sizes between these two extremes could cover vehicle-mounted weaponry, and the application of possible penguin-mortars. The major concern is storage of ammunition, and has led me to believe that frozen penguins would be the best idea. These could be thawed-out on site for use against some targets, or left frozen for a devastating effect on groups of infantry. Although it is theoretically possible to fire live penquins, the resultant death of the bird (and the possible decrease in accuracy) in the firing process makes this a somewhat unnecessary step.

The method by which the penguins are expelled requires the most thought, however. Conventional explosives cannot be used, unless you intend to create a penguin shotgun, spraying shredded flesh and bone over a short distance. A method akin to air rifles is more likely - a short, sharp expulsion of some form of gas. Let us not forget also the advances in air delivery of payloads, and a B-52 Bomber would likely be able to carry an enormous number of all sizes of penguins, both frozen, thawed and still live and kicking. These could be dropped from great heights, and used to carpet-bomb a wide area.

In conclusion, it is highly possible for penguin-based weaponry to become a staple of modern warfare, if necessary steps are taken to train the armed forces in the tactical usage of said weapons.

PS - Dont miss the next installment in the series, 'Cleaning your penguin-cannon, those pesky bits of beak...'

Given the approximate size of most forms of Penguin the most common use for this type of weapon would be Anti tank and Armour piercing rounds. The two major
problems with using penguins as ammunition are of course the propulsion method and the fragility of the Penguin in it's natural state. To overcome these issues I
propose the following:

Propulsion:

The air rifle type method may meet the non-explosive requirements of the device but the range of the weapon must surely suffer as a result. I suggest some sort of an
electromagnetic rail gun setup. This of course would require the Penguin to be at least partially composed of metal. To this end might I suggest a Wolverine type
procedure in which the Penguin's skeletal system would be strengthened using high strength metallic material. This would also aid with the second problem - armour
piercing ability.

Projectile strength:

Obviously the weapon is useless against armour if the Penguin just makes a splat without causing any actual damage (although the enemy may be forced to employ high
strength windscreen wipers on their tanks which may add to maintenance costs). As I have mentioned above the modified high tensileendoskeleton would help the
Penguin pierce the armour of its target but this is just the beginning. Think titanium beak additions with barbed tips, sharpened wing mounted protrusions and explosives.
That's right, explosives. Small incendiary devices could be inserted into the penguin (in a variety of ways) and be rigged to explode on impact. Clearly this would boost
the usefulness of the Penguin in that several purpose built explosive designs could be fielded. Traditional munitions such as bunker busters and cluster bombs could be
rendered obsolete while making the most of Earth's natural resources.

Other areas of development:

With a little research I am sure that many variations on the Penguin weapon can be designed and produced. One of the first versions off the production line would
undoubtedly be the Penguin Torpedo. The sleek shape of the Penguin is perfectly suited to underwater applications and has the added benefit of being a natural sea
creature and therefore harder to detect for an enemy expecting a more conventional torpedo. Of course speed would be an issue but could possibly be overcome by genetically breeding faster Penguins.
The downside to the creation of such a weapon would be the undeniable terrorist threat. The thought of a stolen Anthrax carrying Penguin going off during a Sea world
show is somewhat disturbing and could prove to be a very real threat should this weapon ever go into production.

The Winter Wonderland map of the popular game Half-Life: Opposing Force has the feature of remodeling snarks as deadly penguins. For the unfamiliar, snarks are nasty little one-eyed alien cockroaches which can be carried as weapons. Upon deployment, a snark will enthusiastically seek, chase, and bite nearby players (including you, if you're not careful). After a brief delay, it will explode in a greenish spat of toxic death, similar in strength and appearance to the spore gun projectile. The penguins function identically, except that they explode with the effect and damage of conventional grenades. Close examination of the weapon model (possibly high-definition pack only?) reveals that the penguins in fact have small grenades strapped to their backs.

There is only one pickup for the pengin in Winter Wonderland, next to the only pickup for the displacer. This is on a ledge in more or less plain view, which is reachable only by clever use of the barnacle grapple. The penguin pickup itself appears as a human-sized snowman wearing a top hat and holding a sign which reads "Beware the penguins!".